Implementation of BB84 protocol by QPSK modulation using Mach-Zehnder modulator

We propose to use a dual-electrode Mach-Zehnder modulator for the implementation of the Bennett and Brassard's protocol for quantum key distribution. This implementation allows optical QPSK signals generation with independent base and symbol choices. This signal generation fulfils the constant envelope constrain allowing fainted pulse or continuous variable quantum key distribution.